1. Field of the Invention
The present invention relates to an organic EL (electroluminescence) device, and more particularly, to a hole injection layer of an organic EL device.
2. Discussion of the Related Art
In an organic EL (electroluminescence) device, when electric charges are injected to an organic emitting layer formed between the cathode and anode, hole and electron make a pair, and the pair of hole and electron annihilate, thereby generating light. The organic EL device has been attracted attention as the next generation display device in that it has low driving voltage and low power consumption.
Hereinafter, the related art organic EL device and method for manufacturing the same will be described with reference to the accompanying drawings.
FIG. 1 illustrates the related art organic EL device. Firstly, as shown in FIG. 1, the anode 2 as a first electrode is formed on a transparent substrate 1. At this time, the anode 2 is formed of ITO (indium-tin-oxide). Then, an HIL (hole injection layer) 3 is formed on the anode 2. In this case, the HIL 3 is usually formed of copper phthalocyanine (CuPc).
Subsequently, an HTL (hole transport layer) 4 is formed on the HIL 3. The HTL 4 is formed of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′biphenyl)-4,4′-diamine(TPD) or 4,4′-bis[N-(1-naphthyl)-N-phenyl -amino]biphenyl (NPD).
Next, an organic emitting layer 5 is formed on the HIL 4. At this time, a dopant may be added at needed. Then, an ETL (electron transport layer) 6 and an EIL (electron injecting layer) 7 are sequentially formed on the organic emitting layer 5. The EIL 7 is formed of LiF or Li2O. After that, the cathode 8 as a second electrode is formed on the EIL 7 so that the manufacturing process of the organic EL device is completed.
However, the related art organic EL device has the following disadvantages.
The related art organic EL device has problems of low efficiency and short life span. When driving the related art organic EL device at a high voltage current, the thermal stress generates between the anode 2 and the HIL 3. Thus, the life span of device becomes short due to the thermal stress.
Also, since the organic material used for the HIL 3 has great motility of the hole, a hole-electron charge balance is lost so that quantum efficiency is lowered. That is, in case of the organic EL device requiring the low voltage driving, it is necessary to improve the quantum efficiency for the increase of efficiency. In this respect, the organic material used for the related art HIL is not suitable for improving the quantum efficiency.